Various wholly aromatic polyesters have thus far been introduced because of their outstanding heat resistance and economical material supply. Especially a combination of terephthalic acid with hydroquinone is predominant over other combinations in that it achieves greater economy in attaining high heat resistance. On the other hand, the polyester of the particular combination has not been endowed with easy processability. To this end the polyester requires the addition of a third component of a special structural unit which helps secure a temperature sufficient for easy processing, otherwise it is impossible to achieve an adequate temperature for processing. Incorporation of a hydroxybenzoic acid residue, for example, is of no practical significance since it raises the processing temperature for the polyester to a range above 400.degree. C.